How To Install Blanket (Batts) Insulation
Over Existing Attic Insulation

Valerie M. wrote:

Hey Itchy,

I have an old home with an attic and I am
planning to add insulation to the attic floor. There is a very small layer of
fiberglass insulation already there and I purchased R19 to lay over it. They
sold me kraft paper faced fiberglass batts. Can I lay this over the old stuff?
Do I have the really wrong thing? I live on an island with only ferry boat
access. Please don't make me send it back! What should I do?

Valerie, there are a couple of methods you
could use to add new insulation over existing insulation in your attic - blown
in insulation or batts. Since you have purchased fiberglass batts, I'll cover
that option.

Before you can insulate the attic
you need to make sure it's prepped. Put on your protective clothing, grab a
light and head on up into the attic. You need to inspect it to make sure
everything is right before you start insulating. All of the lower vents need to
be uncovered. If you have existing loose fill insulation it's possible that it
may be covering the vents if baffles (vent chutes) were not installed. If this
is the case it's easier to unclog the vents from the outside of the house using
a leaf blower on the vents to blow the insulation away from them. Once the vents
are clear you need to install baffles.

Next,
take a look at the existing insulation. Make sure it is away from any heat
sources by at least 3". Sources of heat include recessed lighting and metal
chimneys. If you have a bathroom fan make sure it is not covered with insulation
and that it is vented out. This is done by using aluminum flex tubing that
extends from the opening of the fan to one of the upper or lower vents.

Is
your home very old? If you have frayed or degraded wiring or the old knob and
tube wiring DO NOT PLACE INSULATION OVER IT. This is a extreme fire hazard and
you will need to call a electrician to update your electrical wiring
system.

You
will also need to determine how much insulation is required for your neck of the
woods. You can ask your local building code department or look at the comparison
chart.

You don't
want to use kraft faced batts to cover existing insulation. The kraft paper acts
as a vapor barrier and can trap moisture that will cause damage to the attic
structural members. When using fiberglass batts to reinsulate the attic make
sure they're unfaced. If the existing insulation is level with the top of the
ceiling joists it's best to install the batts perpendicular to the existing
ones. The reason for this is that it will completely cover the joists and will
provide a better thermal coverage. I like to stock the attic first. Start laying
the fiberglass blankets at the far end of the attic and work your way back. Make
sure they are placed snug against each other with no gaps and try not to
compress them as it will reduce the r-value. Use a utility knife to make cuts in
the batts in areas where they don't fit. Scrap pieces can be used to fill any
gaps or voids. Once the attic has been insulated,
don't forget to insulate the attic hatch cover.

Finally,
remember safety first. Make sure you are walking only on the joists. Don't
try walking on the sheetrock or you will soon find yourself on the floor below
you. Make sure the attic area is well lit and always wear protective clothing
and a dust mask.